Factor VIII related antigen (F.VIIIR:Ag.) has been found on and within normal platelets. This pool of F.VIIIR:Ag is felt to be intrinsic to the platelet and non-exchangeable with circulating plasma F.VIIIR:Ag. Any interaction of this platelet F.VIIIR:Ag with plasma coagulation factors is merely speculative at this time. This project seeks to quantitate the amount of F.VIIIR:Ag located on/within the platelet and identify the site(s) at which is located and any role it may play during platelet activation and plasma coagulation activation.